Particles on droplets: From fundamental physics to novel materials

We review the phenomenon of adsorption of colloidal particles at interfaces between two immiscible liquids, such as on the surfaces of droplets. Though the tendency of small particles to adsorb at liquid interfaces has been under investigation for nearly a century, attention to many aspects of the problem has recently grown, in part because of the tremendous potential for materials development. From a fundamental point of view, fluid interfaces offer substantial complexity because electrostatic and other inter-particle forces can create long-range deformation of the interface, which in turn drastically alters the interactions among the particles. Nonetheless substantial progress has been reported in the literature on topics including the energetics of adsorption, the interactions among adsorbed particles, and the modulus of concentrated layers. Particles at interfaces can serve as a useful experimental model system for a number of fundamental questions of statistical mechanics. For materials development, assembly of particles on droplets is attractive for the extraordinary architectural control it offers and the broad range of particles and solvents that can be used.